Sleep apnea is a syndrome in which the structure of the airway changes during sleep, resulting in periods of apnea. Although the initial symptoms are related to the apnea and loss of sleep, the prolonged periods of hypoxia due to the apnea eventually result in profound physiologic changes. One commonly-diagnosed sleep apnea syndrome is obstructive sleep apnea (OSA). OSA may be defined as the absence of air flow combined with persistent respiratory effort during sleep. While the upper airway normally remains patent during quiet breathing and wakefulness in sleep, patients with OSA can have repetitive periods of upper airway closure during sleep. The upper airway closures usually occur at various sites in the pharynx.
Areas responsible for inducing OSA, seen in FIG. 1, are considered to be the nose 1, the nasopharynx 2, the soft palate 3, the uvula 4, the palatal tonsils 5, the lateral and posterior walls of the pharynx 6 and 7, respectively, and base of the tongue 8. Stenosis of the airway in each area alone, or in combination, can result in apnea during sleep. However, other areas also may be involved in producing OSA. The patency of the potentially-collapsible pharynx 9 during inspiration depends on the balance between subatmospheric pressure in the pharyngeal airway 9 and airway-dilating forces generated by the pharyngeal muscles 6,7. The pressure required to collapse the upper airway in the absence of upper airway muscle activity is normally subatmospheric.
OSA is not a benign disease. It has been estimated that, in one year, 58,000 motor vehicle accidents involved a sleep apnea patient. These patients also have a higher incidence of stroke, right heart failure, and an increased mortality rate when there are greater than 20 apneic episodes per hour of sleep. Sleep apnea patients tend to have irresistible "sleep attacks" and higher incidence of anxiety, depression, and sexual dysfunction.
In general, the principle of OSA treatment is to remove the upper airway obstruction, most likely a pharyngeal occlusion. Although the treatment regimen must be tailored to the individual, his symptoms, sleep study results, and physical findings, therapeutic options tend to fall into four broad categories. First, aggravating factors such as alcohol or sedatives are identified and eliminated, and the patient undergoes sustained weight reduction.
Second, pharmacologically-active substances such as protriptyline and pilocarpine may be used. One example of a method for treating sleep apnea using pharmacologically-active agents may be found in U.S. Pat. No. 5,407,953 to Morgan in which sleep apnea is treated by administering a compound that results; in the release of pilocarpine to the nasopharynx and hypopharynx in an amount effective to improve the tone of the pharyngeal musculature, thus reducing or eliminating sleep apnea. However, the administration of certain pharmacologically-active substances may be contraindicated in some patients, or may cause unexpected side effects.
Third, surgical intervention such as transtracheal oxygen therapy (TTO), uvulopalatopharyngoplasty (UPPP), tracheotomy, and even suction-assisted lipectomy, may be employed.
Fourth, mechanical and prosthetic devices including continuous positive airway pressure (CPAP), bi-level positive airway pressure (BiPAP), and dental appliances that advance the mandible forward during sleep or that reposition the tongue, can be used. One example of a mandible-repositioning dental appliance is found in U.S. Pat. No. 5,409,017 to Lowe. This appliance forces the lower mandible outward and attempts to maintain airway patency.
One of the most effective treatments for OSA involves the use of a mechanical device such as CPAP or BiPAP. When used appropriately, positive airway pressure methods tend to raise the pharyngeal pressure above the closing pressure, thereby overcoming the pharyngeal obstruction. Because CPAP and BiPAP devices may produce nasal stuffiness and feelings of claustrophobia, patient compliance often is a problem. Indeed, some estimates place actual patient compliance with CPAP and BiPAP devices at less than 50 percent. Although it is still unknown how much CPAP or BiPAP use is sufficient to prevent daytime hypersomnolence, sleeping without positive airway pressure for one night can reverse the beneficial effects of one month of positive airway pressure use.
One example of a positive airway pressure breathing gas delivery method and apparatus is found in U.S. Pat. No. 5,433,193 to Sanders, et al. This device treats sleep apnea through the application of alternating high and low level positive airway pressure within the airway of the patient, with the high and low airway pressure being coordinated with a spontaneous respiration of the patient.
Many treatment modalities are ineffective for certain patients. Furthermore, the many effective methods often are sufficiently obtrusive as to adversely impact patient compliance and, therefore, the actual effectiveness of the treatment. What is needed, then, is an apparatus and method for reversibly modifying the shape of a selected portion of the body such as, for example, the pharynx, to produce a desired result, for example, to overcome obstructive sleep apnea by urging open the pharynx.